In U.S. Pat. No. 4,360,728, Drexler describes a data card having a laser recording, direct-read-after-write (DRAW) strip, alongside a magnetic strip, the two strips working in cooperation. Maurer et al. in U.S. Pat. No. 4,467,209 discloses an identification card having erasable and non-erasable data. The erasable medium is suggested to be magnetic, while the non-erasable medium is a laser recording material or an integrated circuit. Neither of these cards is sufficient since both permit alterations or additions to be made on either strip after the cards have been produced. The ability to make alterations and additions on the magnetic strip is desirable. But it is not necessarily a desirable characteristic for the data storage strip. This capability means increased cost. It is one of the objects of the present invention to reduce costs in the production of data cards. Furthermore, there are data card uses for which it is best not to permit alterations or additions after entries into data storage.
Dil, in U.S. Pat. No. 4,209,804, teaches a reflective information recording structure which contains prepressed V-shaped grooves in which data may be recorded by local melting of the reflective metal coating by a laser. The data on the media is read by means of optical phase shift effects. Since the preformed grooves are at an optical phase depth of 95.degree. to 140.degree., the reading laser must be of the precise wavelength corresponding to the groove depth. The information area has a width of approximately 0.6 microns, so a thick protective substrate, usually 1200 microns deep is used to ensure that one micron surface dust particles are out-of-focus for the read beam.
Such thick protective materials cannot be used for wallet cards which have a total thickness of only 800 microns under ISO (International Standards Organization) standards and further it would be uncomfortable to carry a rigid card in trouser pockets or wallets. Also, it is difficult to bond a phase sensitive recording/reading surface to a protective laminating material with an adhesive without introducing a varying phase shift across the surface. It is also impractical to melt large holes since a large lip would be formed around the hole causing a great distortion of the phase shift. Edge transition of the hole is the phase shift which is measured, and since the height of the lip is directly proportional to the square root of the hole diameter, phase shift reading is only practical for small holes. For example, a 25 micron diameter hole creates a lip with one micron height, which is much larger than the wavelength of the reading beam. Thus for large holes and bonded protective materials it is desirable to have a recording/reading structure that does not rely on phase shifts.
Lahr in U.S. Pat. No. 3,873,813 teaches a debit card in which use is indicated by alteration of a spot of heat sensitive coating in a selected area thereby permanently changing the reflective characteristics of that area. A reflective heat sensitive material becomes transparent on heating, thereby exposing an underlying strip of black paper which then absorbs the light energy. Recording requires exposure to a high intensity light beam for 0.7 second to raise the temperature of the material to 175.degree. F. and an additional 5 milliseconds above 175.degree. F. This type of credit card system permits recording of less than two data bits per second. Because of the retained, diffused liquid, the sizes of the data spots are large and difficult to regulate. This card requires a blue read beam, therefore scratches and surface dust will cause a large number of data errors unless very large data spots are used that reduce capacity to under 10,000 bits. While this data capacity is satisfactory for some debit and credit cards, it is unsuitable for detailed recording of financial, insurance, medical and personal records.
Various recording media have been developed for use on a rotating disk format. Because the disk is spinning rapidly, short laser pulse times (on the order of 500 nanoseconds) are necessary to confine the heating to small spots. The media have been developed to increase the sensitivity to the beam by varying the parameter of media absorptivity. Spong in U.S. Pat. Nos. 4,190,843 and 4,305,081 puts an absorptive dye layer over a reflective aluminum layer. Spots are recorded by ablation of the dye layer exposing the underlying reflective layer. Bell in U.S. Pat. No. 4,300,143, teaches a similar technique. Bartolini in U.S. Pat. No. 4,313,188 adds a protective layer between the dye layer and the reflective layer. Wilkinson in U.S. Pat. No. 4,345,261 uses a light absorptive silica dielectric layer in place of the dye layer. Terao teaches an inorganic absorptive layer over an organic recording film layer. Holes are formed in the film layer by heat generated in the absorptive layer. Suzuki in U.S. Pat. No. 4,202,491 uses a fluorescent ink layer on which data spots emit infrared radiation. Magneto-optical erasable laser recording materials are also known in the art. For example, see U.S. Pat. No. 4,493,887 to Peeters et al. Improved sensitivity is obtained in these media at the expense of extra layers which increase complexity and cost. This increased sensitivity is not necessary for a card format.
Bouldin et al. discloses one suitable method for photographically replicating information on the optical data storage medium of the present invention. The information is copied when actinic radiation is shown through transmissive areas of a master onto a silverhalide emulsion photosensitive medium. The medium is then developed. A laser is used to read the changes in reflectivity resulting from the process.
In the field of information storage there is sometimes a need to use two complementary databases. An object of the present invention is to devise a data card suitable for use with such databases.